Inhibitory effect of sericin on polyphenol oxidase and its application as edible coating

Sericin, a water-soluble globular protein derived from silk industry wastewater, was investigated for food industrial applications. The results proved that sericin retarded polyphenol oxidase (PPO) activity. However, the degree of inhibition varied depending on the enzyme origins, the types of substrate, sericin content and sericin molecular size. Using catechol as a substrate, under the conditions studied, sericin lowered purified mushroom PPO and apple extract PPO activity by 40% and mango extract PPO by 75%. Kinetic studies on purified mushroom PPO indicated that the type of inhibition of sericin was dependent on the substrates used. Inhibitory effects of sericin increased as the sericin content increased. The reduction in sericin molecular size by enzymatic hydrolysis produced sericin hydrolysate with ability to decrease PPO activity approximately three times greater than that of sericin. Fresh-cut Red Delicious apples coated with sericin showed significant reduction in weight loss and improvement in the colour and texture.